Currently, a cold-cathode fluorescent lamp (hereinafter referred to as a CCFL) is widely used as a light source for a liquid crystal display apparatus. Generally known backlight methods using the CCFL are: an edge light method in which light from the CCFL enters a light guide plate from its side surface, and is outputted from a front surface of the light guide plate as substantially uniform planar light, so that the planar light illuminates a liquid crystal panel from its back surface; and a method of illumination directly from below, in which a plurality of CCFLs are arranged on a back surface of the liquid crystal panel to thereby directly illuminate the liquid crystal panel with the light of the CCFLs.
In recent years, from the viewpoint of the environmental issues or electrical power saving, image display devices are being developed which utilize, as light sources free from mercury and with lower power consumption, light sources formed of semiconductor materials such as a light emitting diode (LED) and a laser diode (LD). Particularly, the laser sources can be a light source most suitable for image display devices in terms of not only their low electric power consumption, but also image quality, for example, a wide color reproduction range. Moreover, the laser sources are advantageous from the viewpoint of downsizing and simplification of the light source in an image display device, since a light output of a W class can be achieved with a single laser source.
In addition, in order to configure a thin liquid crystal display apparatus, a light box or a light guide plate is generally applied. For example, as a liquid crystal backlight using the light guide plate, a liquid crystal display apparatus is proposed in Patent Document 1. In the liquid crystal display apparatus disclosed in Patent Document 1, LEDs are fixed at both ends of a light guide rod, and light from the LEDs are reflected by triangle grooves provided on a surface of the light guide rod on the side opposite to the light guide plate. The light is guided to the light guide plate, and is then reflected by a prism array formed on a reflection surface which opposes a light exiting surface of the light guide plate, thereby to improve the transmittance of light passing through a polarizing plate of a liquid crystal panel.
Further, proposed are liquid crystal backlights which realize illumination having a uniform light amount distribution and low power consumption, which are achieved with an improvement in the arrangement of laser sources and in optical systems (see Patent Documents 2 and 3).
Further, proposed is a technique in which laser light from a laser source is combined in a light guide plate by using at least two optical lenses, and the polarization direction of the laser light is adjusted with respect to the polarization direction of a light entering side of a liquid crystal panel (see Patent Document 4).
Further, proposed is a technique in which a red light component, a green light component, and a blue light component included in light emitted from a light source are separated in a light guide plate so as to be outputted, respectively, to red sub-pixels, blue sub-pixels, and green sub-pixels in a liquid crystal panel, whereby light elements absorbed by a color filter in the liquid crystal panel are reduced and high efficiency is achieved (see Patent Document 5).